Method of producing sulfate granules and volatile acid gases

ABSTRACT

A METHOD OF AND APPARATUS FOR PRODUCING SULFATE SALTS AND A VOLATILE ACID GAS BY PROVIDING INTIMATE CONTACT BETWEEN FLUIDIZE SALT PARTICLES AND A SPRAY OF SULFURIC ACID IN A REACTION ZONE MAINTAINED AT ELEVATED TEMPERATURE. THIS ABSTRACT IN NEITHER INTENDED TO DFINE THE INVENTION OF THE APPLICATION WHICH, OF COURSE, IS MEASURED BY THE CLAIMS, NOR IS IT INTENDED TO BE LIMIING AS TO THE SCOPE OF THE INVENTION IN ANY WAY.

Feb. 16, 1971 (3. W. CANNON METHOD OF PRODUCING SULFATE GRANULES AND VOLATILE ACID GASES Filed Feb. 28, 1967 3 Sheets-Sheet 1 JEPARA 70/? REACTOR [NI/TOR Feb 16, 1971 '0. W. CANNON 3,5fi3,7m

METHOD OF PRODUCING SULFATE GRANULES AND VOLATILE ACID GASES Filed Feb. 28, 1967 5 Sheets-Sheet 2 Jl/ZPf/ATE M70000 INVENTOR ATTORN Y Feb. 16, 1971 c. w. CANNON 1. f

METHOD OF PRODUCING SULFATE GRANULES AND VOLATILE ACID GASES Filed Feb. 28. 1967 3 SheetsSheet 5 (0/ f/J W. ('0/7/70/7 INVEN TOR 3,563,701 METHOD OF PRODUCING SULFATE GRANULES AND VOLATILE ACID GASES Curtis W. Cannon, Boulder, Colo., assignor to Climax Chemical Company, Monument, N. Mex., a corporation of Delaware Filed Feb. 28, 1967, Ser. No. 619,434 Int. Cl. C01d /02; C01g 1/10 US. Cl. 23-117 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to an improved method of and apparatus for producing sulfate salts and the volatile acid gas from sulfuric acid and the feed salt containing the more volatile acid radical. As used herein, the term sulfates shall mean those salts produced by reaction between sulfuric acid and the corresponding feed salt.

Prior to the present invention, several types of methods have been used for reacting sulfuric acid and salts such as sodium chloride. In one type, the sulfuric acid and the salt are reacted in a rotary furnace directly in contact with combustion gases to supply the necessary reaction temperature. Excessive lumping of the sulfate product occurs, and the hydrochloric gases are considerably diluted by the large amount of combustion gases necessary to maintain the reaction temperature. In another type, such reaction takes place in a muflie type furnace with rotary rakes. Such furnaces have structural limitations which restrict capacity of single units and produce a poorer grade of sulfate than the method to be described. In a further method, the reaction takes place in a granular bed maintained at reaction temperatures by hot combustion gases, containing sulfur trioxide or sulfuric acid vapors, to maintain the bed in a fluidized state and if sulfuric acid is used, this method requires the use of an acid vaporizing chamber. This third method produces a uniform powder-like sulfate of high quality but for some purposes, the sulfate is excessively dusty. It is preferred that it be in the form of coarser particles and granules having freer flowing characteristics.

It is therefore an object of the present invention to provide an improved method of and apparatus for producing a more granular and free-flowing sulfate product and a volatile acid .gas from the reaction of sulfuric acid with a salt feed containing the more volatile acid radical.

Another object of the present invention is to provide an improved method of producing sulfates from sulfuric acid in a fluidized bed with a minimum production of fines.

Another object is to provide an improved method of and apparatus for producing sulfate granules from sulfuric acid in which the sulfate granules have a high density and are a free-flowing product which is easily handled.

Another object is to provide an improved method of commercially producing a sulfate product of very high purity.

A further object is to provide an improved method of reacting sulfuric acid and a fluidized salt feed at elevated temperatures in which losses of sulfuric acid due to de- United States Patent 0 Patented Feb. 16, 1971 composition at such temperatures in the vapor phase is substantially avoided.

A further object is to provide an improved apparatus for providing intimate contact of sulfuric acid with fluidized salt particles.

Still another object is to provide an improved method of and apparatus for producing a granular sulfate product in a fluidized bed reaction zone from sulfuric acid which eliminates the use of an acid vaporizing chamber.

Still a further object is to provide an improved method of and apparatus for producing sulfates from liquid sulfuric acid by which construction is simplified and maintenance of the equipment is minimized.

The present invention contemplates the production of a sulfate and a volatile acid gas from the reaction of sulfuric acid with a salt containing a more volatile acid radical. Examples of these salts are sodium chloride, potassium chloride, calcium fluoride and calcium phosphate. When reacted wtih sulfuric acid, these salts produce sulfates of sodium, potassium and calcium and the corresponding volatile hydrochloric, hydrofluoric and phosphoric acid gases. In the following description of the process only one salt, sodium chloride, is used; it being understood that such description is illustrative of the process using other suitable salts.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the present invention are hereinafter set forth in the description of the forms of the invention shown in the drawings wherein:

FIG. 1 is a schematic flow diagram illustrating the preferred form of the present invention.

FIG. 2 is a detail elevation view of the lower end of the vessel defining the reaction zone and the preferred form of apparatus for introducing the feed components and heating medium into the reaction zone.

FIG. 3 is a partial sectional view of the feed apparatus shown in FIG. 2.

FIG. 4 is a plan view of the feed apparatus taken along line 44 in FIG. 3.

FIG. 5 is an elevation view partly in section of a modified form of feed apparatus.

FIG. 6 is a partial sectional view illustrating a further modification of the feed apparatus shown in FIG. 5.

FIG. 7 is a sectional view of the grate structure over the sulfate outlet taken along line 7-7 in FIG. 2.

Referring more in detail to FIG. 1, the reactor 10, which defines the reaction zone is provided with an eccentric conical bottom 12. The feed apparatus 14 extends through the bottom 12 into communication with the reaction zone and as hereinafter described in greater detail is adapted to supply a spray of liquid sulfuric acid, salt particles and heated gas to said reaction zone. Sulfuric acid is pumped through line 16 from a suitable source (not shown) to feed apparatus or sparger 14. Salt particles entrained in a gas stream are supplied through line 18 to feed apparatus 14. Hot gases are supplied through line 20 to the feed apparatus 14- from a suitable source (not shown) such as a furnace and blower.

To provide the desired reaction and to minimize the production of bisulfates and oversize agglomerates it is preferred that the temperature in the reaction zone be maintained in the range of 700 F. to 1000 F. To maintain such reaction temperatures, temperatures of the hot gases will be between 1600 and 2000 F. Hot air or gas used to feed the salt may have a temperature approaching the melting point of the feed salt, but care should be taken to assure that the salt particles are not heated to their softening point as they can fuse, block the salt passages, and form crusts which would interfere with the salt feed. If desired, the entrained salt particles and the hot gases may be combined immediately before their discharge from the feed apparatus 14 into the reaction zone. To obtain proper spraying of the acid with a conical type spray, it is believed that the acid should be under a pressure in the range of 200 p.s.i. to 500 p.s.i. The combined volume of gas being fed to the reaction zone is preferred to be suflicient to maintain the unreacted and partially reacted salt particles fluidized while allowing the sulfate granules to settle in the lower end of the reaction zone to be discharged therefrom. This gas sweeps the acid gas and the fines upwardly through the reaction zone and through line 22 into separator 24. Separator 24 is of any suitable design to remove the fine solids from the gases. The gases including the hydrochloric gas are discharged from separator 24 through line 26 and may be conducted to suitable equipment (not shown) for the recovery of the hydrochloric gas from the other gases. The solids separated from the gases in separator 24 are discharged therefrom through line 28 by discharge valve 29. These undersized sulfate particles may preferably return to the reaction zone for agglomeration by entrainment in the salt feed tllowing through line 20. A portion of the hot product gases may be recycled and used to supply the gas for heat and fluidization so that suflicient gases for the transport and fluidization are available without unnecessary dilution of the product gases with excess air.

As hereinafter described, the sulfuric acid is supplied to the reaction zone as a liquid spray. However, it has been discovered that as much as sixty percent of the stoichiometric amount of sulfuric acid may be supplied to the reaction zone as vapors in the hot gas feed with the remainder of the acid being supplied as a liquid spray without sacrificing the advantages previously mentioned. This utilization of acid vapors is particularly advantageous when such vapors are available from a sulfuric acid plant converter. It will be appreciated that sulfuric acid plant converter gases are adequate in volume to maintain fluid or transport velocities in fluidized reactors and that the dilution of these gases with excess air, combustion products and inert gases from the air is sufficient. This same effective dilution can be obtained by introducing an excess of air, combustion gases or recycle product gases, even when all or part of the sulfuric acid is injected as a liquid. Utilization of such converter gases is economical since such gases are available in suitable concentration for use in the present process and are available at elevated temperatures. It has been found that the use of a substantial percentage of the sulfuric acid feed to the fluidized bed reaction zone as liquid will substantially produce the desired agglomeration of the particles into free-flowing granules.

The lower end of bottom 12 of reactor connects with discharge lines 30 and 32. Suitable means s provided to separate the oversize sulfates to be discharged through line 30 under control of valve 34 while the sulfate granules are discharged from line 32 under control of valve 36.

It has been found that by spraying the liquid sulfuric acid into the fluidized salt in the reaction zone and by substantially surrounding the acid spray with the hot gas and/or salt feed streams in the reaction zone, the reaction may be carried essentially to completion in a single stage with 93 to 98 percent of stoichiometric yields. Additionally, the size of the sulfate granules is affected by adjustment of the spray position and the liquid acid pressure as well as by controlling the reaction zone temperatures and the recycle of fines to the reaction zone. This method results in the production of globular sulfate granules of higher density which have free-flowing characteristics and reduced tendency to cake as compared to the finer sulfate product produced by the vapor acid feed process.

This form of feeding of the liquid sulfuric acid to the reaction zone while providing a shield of hot gases and salt around the sulfuric acid spray, protects the walls of reactor 10 from direct contact with the unreacted acid, eliminates massive agglomeration and minimizes corrosion conditions in the reactor 10.

The feeding apparatus or sparger 14 and the eccentric cone bottom 12 of reactor 10 are shown in more detail in FIG. 2. The interior of the bottom 12 is provided with a suitable lining 38. The sparger 14 is supported in position extending through the bottom 12 approximately on the center line of reactor 10 by the support 40. The only significant corrosion occurring is in the vicinity of the initial reaction products and this is minimized by design of the sparger which jets the reaction products into the bed. Thus, no lining is required above the bottom ten to fifteen feet of the reactor and such lining as is used may be a simple acid-proof mortar.

The sparger 14 illustrated in FIGS. 2, 3 and 4 includes an outer shell 42 having a volute inlet 44; an inner shell 46 extending below the outer shell 42, having an inlet 48 and a lower closure 50 through which the acid gas inlet 16 extends; a plurality of tubes 52 set in suitable heat resistant mortar; and the spray nozzle 54 which is adapted to spray the liquid sulfuric acid into the reaction zone as a conical spray immediately above the upper ends of shells 42 and 46 and tubes 52. The lower end of outer shell 42 is suitably sealed as by welding to the exterior of inner shell 46 to direct the flow of the gas and entrained salt particles upwardly through the annular space 56 defined between shells 42 and 46. The volute inlet 44 causes the gas and entrained salt particles to be discharged with a swirling motion which assists in the mixing of the acid spray and the fluidized particles in the reaction zone. It also avoids direct impingement of the salt feed which impingement may result in caking of the salt on the inner shell 46. The tubes 52 provide communication to direct the flow of hot gases delivered into the inner shell 46 by the inlet 48 into the reaction zone. The tubular member 58 surrounds the noule 54 and extends downwardly around line 16 to provide a passage for the insertion of the acid nozzle. A means is provided to adjust the position of nozzle 54 vertically with respect to the tubular member 58. Such means may include the packing gland 60 secured to closure 50 and adapted to tightly seal against and support line 16.

Since some fines which may include unreacted salt particles or small sulfate particles may gravitate into the lower end of the bottom 12 and into the discharge lines 30 and 32, the purge lines 62, 64 and 66 with suitable flow controls are connected to the bottom 12 and lines 30 and 32, respectively, to elutriate and circulate the fines back into the reaction zone.

As previously mentioned, it is desired to avoid discharging the occasional oversize sulfate agglomerates with the sulfate granule product and means such as the grating 68 is provided to separate such oversize sulfates from the product. The grating 68, as shown in FIG. 7, is a series of parallel bars positioned in the juncture between outlets 30 and 32. For example, in outlets of eight inch pipe, the grating bars include three, one-half by two inch bars spaced equally over the juncture area. In this manner, the oversize sulfate agglomerates and other large materials which might block the discharge line 32 or its valve 34 are prevented from entering the discharge line 32. The valve 34, a full opening valve, is opened momentarily every few hours to discharge the oversize sulfates from line 32. The valve 36 controlling discharge of the sulfate granule product may be a star feeder valve to remove the product without disturbing the reaction in reactor 10.

The modified form of feeding apparatus of sparger 70 illustrated in FIG. 5 includes an outer shell 72, an intermediate shell 74 and an inner shell 76 positioned in concentric relationship to each other to provide an outer annular hot gas passage 78, an inner annular salt passage 80 and to surround the nozzle 82 and its feed line 84.

5 A suitable ceramic or other refractory material surrounds the nozzle 82 at the upper end of the feed line 84. Hot air is fed into the passage 78 by the inlet 86 and the volute chamber 88 connecting from inlet 86 to annular hot: gas passage 78. Gas With salt entrained therein is conducted through inlet 90 and volute chamber 92 to the salt passage 80. The two volute chambers 88- and 92 provide the means to impart a rotational movement to the hot gases and the entrained salt feed when discharged into the reaction zone in surrounding relation to the acid spray from nozzle 82.

llttltuttmttm zone. Further exposure of these sulfate fines to liquid sulfuric acid in the reaction zone results in the formation of polysulfates that are sticky or liquid and thereby faci1i tates the agglomeration These pure sulfate granules are believed to be the agglomeration of these particles. The intermediate size less pure sulfate product is believed to be small amounts of incompletely reacted salt surrounded by a sulfate shell. The recycling of the fines into the reaction zone and their subsequent agglomeration into the larger granules in the sulfate product is responsible for 10 the yield of high purity larger sulfate granules.

said hot gas is fed into said reaction zone in surrounding relation to said sulfuric acid spray.

8. The method according to claim 2, wherein said salt particles and said hot gas are fed into said reaction zone in surrounding relation to said sulfuric acid spray.

9. The method according to claim 1, including discharging fine particles from said reaction zone with said volatile acid gas and other gases,

separating said fine particles from said gasses, and

recycling said separated fine particles into said reaction zone.

10. The method according to claim 1, including introducing purge gas into said sulfate granules before their discharge from said reaction zone whereby salt and sulfate particles are elutriated and circulated back to said reaction zone.

11. The method according to claim 2, including recycling said hot gases to said reaction zone,

12. The method according to claim 1, including adjusting the sulfuric acid spray to produce sulfate granules of the desired size.

13. The method according to claim 1 including the step of,

separating the larger, high purity sulfate granules from the remainder of said discharged sulfate granules to provide a high purity sulfate product.

14. The method according to claim 1, wherein said sulfuric acid and said salt particles are introduced into said reaction zone in stoichiometric quantities. 15. The method of producing sulfate granules and a volatile acid gas including the steps of feeding particles of a salt selected from the group consisting of sodium chloride, potassium chloride, calcium fluoride and calcium phosphate into a reaction zone,

feeding hot gas into said reaction zone in sufiicient volume to maintain salt particles in a fluidized state in said reaction zone and a temperature in said reaction zone between 700l,000 R,

spraying liquid sulfuric acid into the fluidized salt particles in said reaction zone whereby a volatile acid gas and sulfate granules are formed,

discharging sulfate granules from the reaction zone,

and

discharging the volatile acid gas from said reaction zone.

References Cited UNITED STATES PATENTS 2,706,144 4/1955 Cannon 23-121 2,706,145 4/1955 Cannon 23-121 3,102,787 9/1963 McMillan et a1. 23-153 25 EARL C. THOMAS, Primary Examiner US. Cl. X.R. 

